by Dag Billger, Owner & Business Manager and Duncan McLeod, Owner & Product Manager at Inertial Sensing
Of late, there has been increasing interest in surveying production blast holes using gyro survey technology. With the growing realization that even holes of only 20 m (66 ft) depth can deviate by a large degree, this interest is only natural. Blast hole surveying to determine the deviation was once the domain of inexpensive, yet inaccurate, mechanical lever systems. But the demand for improved productivity of a mine, and hence from blasting results, means that the precision given by a high-end gyro is increasingly sought after.
The BlastGyro® from Inertial Sensing is the original gyro solution tailor-made for the job. Although several other similar imitations have appeared in the recent years, it is only the original BlastGyro® that has a pedigree stretching back over a decade in the toughest of environments.
Genesis
The BlastGyro® had its genesis in work that was done with the Swedish mining company LKAB in 2012, at the Kiruna mine in northern Sweden. An original isGyro survey instrument was attached to the hose of a charging truck, which was used to survey elevated holes in the mine prior to blasting (Figure 1). This proved invaluable in improving the quality and results of the blasting and the conclusions were presented in 2014 at a conference in Chile.(1)
At this point in time, gyro surveying of blast holes was not widespread. This was partly due to the benefits of precision surveying of blast holes not being widely appreciated at the time. But also, in part, because very lightweight survey gyros did not yet exist. The regular isGyro accomplished the job in situations where it could be mounted on an existing mechanical system, for instance, but it was not suitable for manual use.
By 2014, plans were underway to develop a new line of gyro for the oil & gas market, to survey inside the tubing of production gas holes. It is often necessary to re-survey gas wellbores already in production, but doing it with a conventional large gyro means days of work in removing tubing, surveying, and reinstating the hole. A slim gyro that could enter through a lubricator and fit inside the production tubing would save hundreds of hours of lost production time, labor and material. Thus was born the SlimGyro, and it entered service in Texas in 2015.
The potential application to blasting was quickly seized upon by Inertial Sensing distributor Simon Williams at GyroMax in Australia. At this time, the SlimGyro was still designed to be used with separate 26 mm (1.02 in) running gear, however, its light weight, slimness and ease of use meant it was entirely feasible to be used as a manual system. By attaching the gyro to a commonly available fiberglass rod, wound on a portable feeder reel, it could be comfortably used by a team of two, or even one with simple training.
With systems in operation in Australia and also making its way into Africa, by 2016 the SlimGyro was proving itself to be the go-to choice for operations demanding precision measurements of blast holes. The innate qualities of the SlimGyro lent themselves perfectly to the job, and to this day are unavailable in other systems:
- Low power consumption gives over 80 hours of operation before recharging is required. There is no need to worry about swapping batteries during a shift, or an entire day.
- Memory is practically unlimited. An entire blast ring (or more) can be surveyed in one pass, without pausing between holes for download.
- Oil-field grade precision.
- No limits on latitude, inclination or direction of the holes.
The BlastGyro® name is born
By 2018, the use of the SlimGyro in blasting had gained such acceptance that it was bundled in its own product package, the BlastGyro®. This greatly simplified the logistics of sales and administration, as the name suggests the purpose extremely well. The BlastGyro® had taken off, particularly in Africa, and it was appearing in diverse locales, such as Sweden, Central Asia and Spain (Figure 2).
One shining example is the unit sold to Rosh Pinah Zinc Corporation, then part of Trevali Corporation. In this instance, there was an extensive push to not only utilize the accurate survey results in themselves but to also integrate the data with the results of drone surveying provided by Hovermap from Emesent.(2) In the words of the mine:
‘(The BlastGyro®) has become an integral part of the survey office equipment and contributes immensely to our striving for a safe and productive environment when conducting a survey task.’ Gerhard Louw, Senior Mine Surveyor, Trevali RPZC.
However, development did not stop there. The system has had a major overhaul to make it fully integrated, removing the separate running gear and reducing the diameter to 25 mm (0.98 in) and the weight to under 3 kg (6.61 lb), without compromising on the system accuracy or other characteristics. An added benefit of the fully integrated BlastGyro® is that Bluetooth radio communications are directly available without removing an instrument from a pressure barrel.
The software was updated to incorporate blast plans, allowing the operator to define entire survey campaigns from the office and they were then available on the survey computer. The BlastGyro® surveyor then simply selects the appropriate hole in turn, removing the need to enter survey information on-site. This greatly reduces sources of mistakes in naming and data entry and speeds up surveying.
The BlastGyro® also directly integrates with the SurveySafe™ cloud service, enabling quick and secure transfer of data and QA/QC information between relevant parties once the survey computer picks up an internet connection.
Benefits
A downhole survey instrument must have a suitable length to measure the tangent of the hole, but not be so long as to be heavy and unwieldy; or impossible to get into the hole in the first place! Instruments under 1 m (3.28 ft) in length cannot measure borehole angles accurately, while those approaching 2 m (6.56 ft) are too cumbersome for a blast hole. The BlastGyro® comes in at under 1.5 m (4.92 ft), making it ideal for the job.
The 25 mm (0.98 in) BlastGyro® is the only truly slim gyro available for the job, while similar systems come in at 30 mm (1.18 in) or more.
The BlastGyro® is not dependent on downhole north-finding technology which has important directional limitations.(3) It is therefore usable without loss of accuracy at any latitude on Earth, in holes of any inclination, in any direction and without the need to wait for north-finding shots.
High precision calibration in temperature and alignment means that the results are reliable, run after run. While the goal is to measure the true deviation of blast holes, it is evident that other systems can give a systematic overestimate of how much the drilling has veered from true. It is debatable which is the worse problem: simply assuming a hole is straight, or unknowingly using excessively bent incorrect surveys! The BlastGyro® measures true, as proven in its birth in the deep gas holes of Texas.
Conclusion
Surveying of production blast holes, both underground and in open pits, has come a long way in the last few years. While there are now a number of imitation systems available on the market, only the BlastGyro® combines the necessary elements of true slim design, light weight, long-lasting battery, virtually unlimited survey time, ease of use and proven oil field accuracy. The BlastGyro® began as the only package suitable for everyday manual use in blast holes, but it has consistently remained at the head of the pack as others have imitated it. Of course, it does not stop here, new refinements and innovations are under development.
References
- ‘Methodology for up-hole drilling accuracy measurements at Kiruna SLC mine’. Wimmer, Nordqvist & Billger. 3rd International Symposium on Block and Sublevel Caving (pp. 625-637). Santiago, Chile: Universidad de Chile. Jan 1, 2014
- ‘SlimGyro and Drone Technology – The integration of SlimGyro and drone technology at Rosh Pinah’, Gerhard Louw, Tech*Carnival-23, South Africa. May 2023.
- ‘Similarities between magnetic and north-finding survey tools’, McLeod and Billger, Coring Magazine, Issue 9, 2019.
For more information
Visit: inertialsensing.com
